The gentle giants of Mount Diablo | News | |


The gentle giants of Mount Diablo

Great tarantula migration has begun, and these arachnids are looking for love

Hikers can find tarantulas around the Mount Diablo area typically during the months of September and October. (Photo by Ryan J. Degan)

There are giants lurking on Mount Diablo.

Eight-legged giants who, contrary to popular belief, are harmless to humans -- and just looking for love.

Many tarantulas populate Mount Diablo, and come the end of summer and into the beginning of the fall, these arachnids can commonly be seen scurrying around the mountain searching for a mate.

"They are beautiful creatures and one thing that you learn really quickly, whether it is rattlesnakes or tarantulas or mountain lions, is that these are all really majestic creatures. If you are very respectful of this park, it can all be quite a positive experience," said Ted Clement, executive director of local environmental conservation group Save Mount Diablo.

"I've run into tarantulas with my wife and my kids a number of times, and of course now is the time. You tend to see them in summer and fall but we really love them," he added.

Every year, Save Mount Diablo hosts a series of guided hikes for groups to explore the scenic splendor of Mount Diablo, as well as all of the wildlife that call the mountain home, through its Discover Diablo Series.

One of these hikes -- the Mitchell Canyon Tarantula Hike, held last Sunday -- offered a group of residents the opportunity to explore the mountain and meet a number of these lovelorn spiders.

"We live in San Francisco, and we always wanted to see the tarantula migration or molting or whatever is happening here," Adam Autry said during the hike.

"My first experience was at a 'Sleepy Hollow' haunted hayride and somebody just had a tarantula, and initially I was like any other person, just scared. I didn't have the phobia but I was scared, and the tarantula started crawling on me thanks to the person and it (turned out to be) one of the most calming therapeutic moments I've ever had in my life," added Leslie Martinez, expressing her excitement.

Approximately 40 residents from across the Bay Area attended the hike, and while some hikers were somewhat nervous at the prospect of meeting these spiders, Ken Lavin, a hike leader for Save Mount Diablo, quickly worked to keep their minds at ease.

"It turns out that nobody anywhere has ever been killed by a tarantula, no human ever," Lavin, a naturalist for the Greenbelt Alliance, said right off the bat. "They have venom sacks (but) they are very tiny and not poisonous to humans at all, about enough to take down a cricket."

Lavin went on to explain that the end of summer marks the beginning of mating season for the tarantulas of Mount Diablo and the best time for hikers to spot them out in the open.

"The tarantulas are here all year (but) generally you don't see them. For one, they're nocturnal; No. 2, they're fossorial, which is a great word for they live underground," Lavin added.

Tarantulas will typically spend their lifetimes hiding within their burrows -- which they dig using their fangs -- only emerging when a tasty cricket or beetle ventures close enough for them to leap out and grab.

For males, around the time they turn 7 years old, they will leave their home for the last time in search for a mate, and will continue to search for as many mates as possible until they die of exposure or starvation, which usually takes one to two months.

Tarantulas have eight eyes that look directly up, but a lifetime underground makes their sight mostly useless, Lavin said, which can make searching for a mate quite the challenge. Instead, tarantulas feel vibrations and air currents through their hair that alerts them to what is going on in the world around them.

In order to detect prey, or prospective suitors, that are outside of a burrow, tarantulas place a type of silk that will vibrate, letting them know they have a visitor. In the case of a mate, when a male tarantula approaches a female's burrow and alerts her to his presence, the female will leap out only to have their fangs hooked by special mating hooks located on the male's legs.

Once the mating act is complete, the male tarantula will quickly scurry away in search of another partner, leaving the female to care for their young.

After the male has left, female tarantulas -- who have been known to live for more than two decades -- will stay in her home to take care of the little ones for about one molting cycle, keeping them safe in a silk basket at the bottom of her burrow.

"She'll go down in her burrow, she'll make a sheet of that silk, she'll lay her eggs, and she'll stash the sheet into a basket," Lavin said. "(And) she's a very good mom; she'll take that basket up to get sun and take care of it."

After their first molt, Lavin says it is time for the offspring to go because "they're on momma's nerves, they are on each others nerves and they're not above 'sibling-cide.'"

Spider babies will then head out into the world to dig their own burrows among the wilderness of the Mount Diablo area and begin the cycle all over again.

Tarantulas can be found throughout the Diablo region as well as in Sunol Regional Wilderness and other areas around the East Bay and South Bay -- but act fast to catch a glimpse of the migration because mating season is typically finished by the end of October as male tarantulas die off.

Save Mount Diablo hosts educational events like the Tarantula Hike as one of the many ways the nonprofit advocates for land conservation in Contra Costa County, an area Clement says is in particular danger of having its wildlife and other natural resources compromised by development.

"It's projected that the Bay Area will get about 2 million people in the next couple of decades and a study was done in 2017 looking at all of the Bay Area counties and which of the counties have the most private land at risk for development. And Contra Costa County by far was identified as the Bay Area county with the most private open space at risk of development," Clement said.

"So the bull's-eye is drawn here, and some of those lands that don't have conservation value are prime for development. And we don't have a problem with that, but many of those lands are in incredible areas," he added.

Founded in 1971 -- one year after the first Earth Day -- to help protect these natural resources, Save Mount Diablo officials and their many volunteers work to use land acquisition, environmental stewardship advocacy and educational outreach to really protect open space and natural resources in the area.

Initially starting out with only 6,788 acres of protected land and a single park, today Save Mount Diablo has helped preserve more than 110,000 acres across over 40 parks. And the nonprofit continues to have its sights set on permanently protecting even more land around the mountain.

"Land has been going through a lot of stress from climate change, increased flooding, increased fires, etc. But land (conservation) is actually one of the biggest ways to mitigate against climate change long term," Clement added. "When we protect land in the Mount Diablo area, we are permanently locking up carbon sinks where nature can do its thing ... and that's just critical for us to monitor the crisis that is on our hands."

To learn more about Save Mount Diablo, the Discover Diablo Series or the tarantulas that call the mountain home, visit

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Like this comment
Posted by Tom
a resident of Castlewood
on Oct 11, 2019 at 11:59 am

Very interesting, informative article about tarantulas which I've seen up on Pleasanton Ridge. The background on this better helps us appreciate these hairy little fellas that we've been educated to believe are dangerous but really are not. Thank you for this story.

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